1. Field of the Invention
The present invention relates generally to apparatus for enclosing electrical subassemblies, and more specifically relates to apparatus for releasably securing a subassembly to a chassis of an electrical assembly such as an automobile stereo, compact disc playing mechanism, cassette tape playing mechanism, computer or disk drive mechanism.
2. Description of Related Art
Devices such as automobile stereos or personal computers typically contain subassemblies such as cassette playing mechanisms or disk drives that are attached to a chassis using threaded fasteners. The chassis provides structural support for the subassemblies and also provides electromagnetic shielding to limit electromagnetic interference (EMI) experienced by, and/or created by the device. The fasteners ensure that each subassembly within the chassis is properly located and securely retained within the chassis.
The use of such fasteners can have numerous drawbacks, particularly in a high volume production setting. The fastening process can vary, but there is usually some degree of automation required, ranging from manually loading a screw into a bit on a pneumatic driver to using self-feeding screw machines. Typically, the torque applied by the device used to drive the fasteners must be monitored daily and adjusted in order to assure proper seating of the fasteners. When fasteners are used, sheet metal tolerances have to be maintained at tight levels to allow for the minimization of stress in the assembly when aligning multiple fasteners with corresponding holes in the chassis and the subassembly.
When threaded fasteners are used to assemble an electrical device, the assembly cycle time can be very long especially in high volume production. An operator assembling the device must typically obtain the threaded fastener, bring it in contact with the driver bit, then drive the threaded fastener. Furthermore, using threaded fasteners presents a risk of any one or more of the following upstream failures occurring: stripping of threads; insufficient torque resulting in an unseated fastener; foreign object damage due to fasteners and/or metal shavings dropping into the assembly and/or subassembly; and stripping the head of the threaded fastener. Also, a fastener installation tool such as a driver and bit can slip off the fastener and impact an electrical component resulting in a damaged assembly.
If self-tapping fasteners are used, the process of driving the self-tapping fasteners into sheet metal often causes shavings of sheet metal to disperse into the assembly. Such shavings have been known to cause electrical failures that can permanently damage the product. If self-tapping fasteners are not used, an extra production step is necessary to form threads in the sheet metal of the chassis and/or the subassembly to be installed within the chassis.
Fasteners further require an additional inventory burden on the production line in that the production line must be continuously stocked with part numbers (fasteners) other than the integral components that add value to the assembly. Also, special tools specifically required for assembly using fasteners, such as drivers and bits, must be continuously monitored and maintained for proper performance, wear and torque specifications. Typically, the top and/or bottom surface of the chassis must be secured in place after the subassembly is attached to the chassis.
Special fixtures are often required on the production line to hold a subassembly in the proper location while it is mounted within the chassis with fasteners. Such fixtures can be very complex, and the use of such fixtures usually requires extra handling of both the subassembly and of the resulting assembly thereby adding to the production cycle time and potentially compromising quality of the final product.
Sometimes tabs are cut and bent out of the chassis in order to retain a subassembly. However, when the tabs are small, they are typically too weak to be effective, and when the tabs are large, openings formed when each tab is bent provides a channel for EMI into and out of the chassis.
Accordingly, there is need for electrical assemblies that do not require fasteners, fixtures or tooling for the process of securing subassemblies into a chassis while still providing structural integrity and adequate shielding to minimize EMI. Such assemblies can provide for improved assembly line efficiency and improved product quality.